Method and apparatus to determine mobile user's location in a wireless communication network

• US 6,788,945 B1
• Filed: 07/23/2002
• Issued: 09/07/2004
• Est. Priority Date: 07/23/2002
• Status: Expired due to Term

• Current Assignee: Calamp Wireless Networks Inc. (CalAmp Corporation)
• Original Assignee: WorldCom, Inc. (Verizon Communications Inc.)
• Inventors: Paris, Alan T., Echols, Billy G. Jr.
• Primary Examiner(s): GELIN, JEAN ALLAND
• Application Number:
  US10/201,728
• Time in Patent Office: 777 Days
• Field of Search: 455/404.2, 455/405, 455/414.2, 455/422.1, 455/440, 455/441, 455/456.1, 455/456.2, 455/456.3, 455/502, 342/351.16, 342/357.09, 342/458, 342/357.06, 342/357.01, 342/357.05, 370/510, 370/512, 370/328, 370/338, 370/337
• US Class Current: 455/456.5
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A wireless communication system and method for determining a location of a mobile station communicating within the system. The system comprises a plurality of base receivers for receiving wireless communication, a controller, and at least one mobile station for transmitting a signal for receipt by at least two of the base receivers. The base receivers that received the transmitted signal determine a timing error associated with the transmitted signal, and the controller determines a separation distance between the mobile station and each base receiver that received the transmitted signal based at least upon the timing error. The controller further determines the location of the mobile station within the wireless communication network based upon the separation distance between the mobile station and the base receivers that received the transmitted signal.

Claims

1. A method for determining a location of a mobile station within a wireless communication network, the wireless communication network including a plurality of base receivers coupled to a switch for receiving communication from the mobile station during a specified period of time, the method comprising:

transmitting a signal from the mobile station for receipt by at least two of the base receivers;

determining a timing error associated with the transmitted signal for each of the base receivers that received the transmitted signal;

determining a separation distance between the mobile station and each base receiver that received the transmitted signal based at least upon the timing error; and

determining the location of the mobile station within the wireless communication network based upon the separation distance between the mobile station and the base receivers that received the transmitted signal, wherein determining the location of the mobile station, further comprises;

determining a circular region around a location of each base receiver that received the transmitted signal, each circular region having a radius equal to the separation distance between the mobile station and the respective base receiver; and

determining an intersection point of the circular regions, thereby providing the location of the mobile station in the wireless communication network.

2. The method of claim 1, wherein determining a timing error further comprises:

determining a difference in time that the mobile station transmitted the signal and the specified time period that the mobile station should have transmitted the signal.

3. The method of claim 1, further comprising:

forwarding the determined timing error and message content that was received in the transmitted signal from each base receiver that received the transmitted signal to the switch.

4. The method of claim 1, further comprising:

determining the number of base receivers that received the transmitted signal from the mobile station.

5. The method of claim 1, further comprising:

calculating the difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal.

6. The method of claim 1, wherein determining a timing error further comprises:

determining a plurality of filter coefficients to match the signal transmitted by the mobile station to a predefined synchronous bit pattern;

continuously convolving the plurality of determined filter coefficients with the signal transmitted by the mobile station until a predefined recognition pulse is output by the convolution; and

determining a difference in time that the predefined recognition pulse is output and the specified time period that the mobile station should have transmitted the signal.

7. The method of claim 6, wherein determining a plurality of filter coefficients to match the signal transmitted by the mobile station to a predefined synchronous bit pattern further comprises:

removing a carrier frequency from the signal transmitted by the mobile station, thereby providing a resultant modulating signal;

computing a spectrum of the resultant modulating signal;

performing frequency domain filtering of the spectrum to derive a dual Hilbert transform, thereby determining a phase of an intermediate subsidiary function;

setting a magnitude of the intermediate subsidiary function;

correcting for non-causality and long-range causality of the intermediate subsidiary function; and

placing the removed carrier frequency back into the signal transmitted by the mobile station.

8. A method for determining a location of a mobile station within a wireless communication network, the wireless communication network including a plurality of base receivers coupled to a switch for receiving communication from the mobile station during a specified period of time, the method comprising:

transmitting a signal from the mobile station for receipt by at least two of the base receivers;

determining a timing error associated with the transmitted signal for each of the base receivers that received the transmitted signal;

determining a separation distance between the mobile station and each base receiver that received the transmitted signal based at least upon the timing error; and

determining the location of the mobile station within the wireless communication network based upon the separation distance between the mobile station and the base receivers that received the transmitted signal, wherein the determining the separation distance comprises;

calculating a difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal, and

averaging the calculated difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal.

9. The method of claim 8, further comprising:

subtracting the averaged difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal.

10. The method of claim 9, wherein determining a separation distance, further comprises:

determining a separation distance between the mobile station and each base receiver that received the transmitted signal by dividing the subtracted averaged difference by a factor.

11. The method of claim 10, wherein determining the location of the mobile station, further comprises:

plotting a circular region around a location of each base receiver that received the transmitted signal, each circular region having a radius equal to the separation distance between the mobile station and the respective base receiver; and

determining an intersection point of the plotted circular regions, thereby providing the location of the mobile station in the wireless communication network.

12. A wireless communication system for determining a location of a mobile station communicating therein, comprising:

a plurality of base receivers configured to receive wireless communication;

a controller; and

a mobile station configured to transmit a signal for receipt by at least two of the base receivers, wherein;

the base receivers configured to receive the transmitted signal are further configured to determine a timing error associated with the transmitted signal, and the controller is configured to determine a separation distance between the mobile station and each base receiver that received the transmitted signal based at least upon the timing error, and is further configured to determine the location of the mobile station within the wireless communication network based upon the separation distance between the mobile station and the base receivers that received the transmitted signal, and

the controller is further configured to determine a circular region around a location of each base receiver that received the transmitted signal, each circular region having a radius equal to the separation distance between the mobile station and the respective base receiver, and is configured to determine an intersection point of the circular regions, thereby providing the location of the mobile station in the wireless communication network.

13. The wireless communication system of claim 12, wherein the timing error is a difference in time between the mobile station transmitting the signal and a specified time period at which the mobile station should have transmitted the signal.

14. The wireless communication system of claim 12, wherein the base receivers that are configured to receive the transmitted signal are further configured to forward the determined timing error and message content received in the transmitted signal to the controller.

15. The wireless communication system of claim 12, wherein the controller is further configured to determine a number of base receivers that received the transmitted signal from the mobile station.

16. The wireless communication system of claim 12, wherein the controller is further configured to calculate a difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal.

17. The wireless communication system of claim 12, wherein the controller is further configured to determine a plurality of filter coefficients to match the signal transmitted by the mobile station to a predefined synchronous bit pattern, to continuously convolve the plurality of determined filter coefficients with the signal transmitted by the mobile station until a predefined recognition pulse is output by the convolution, and to determine a difference in time that the predefined recognition pulse is output and the specified time period that the mobile station should have transmitted the signal.

18. The wireless communication system of claim 17, wherein the controller is further configured to:

remove a carrier frequency from the signal transmitted by the mobile station, thereby providing a resultant modulating signal;

compute a spectrum of the resultant modulating signal;

perform frequency domain filtering of the spectrum to derive a dual Hilbert transform, thereby determining a phase of an intermediate subsidiary function;

set a magnitude of the intermediate subsidiary function;

correct for non-causality and long-range causality of the intermediate subsidiary function; and

place the removed carrier frequency back into the signal transmitted by the mobile station.

19. A wireless communication system for determining a location of a mobile station communicating therein, comprising:

a plurality of base receivers for receiving wireless communication;

a controller; and

a mobile station configured to transmit a signal for receipt by at least two of the base receivers, wherein;

the base receivers are configured to receive the transmitted signal and to determine a timing error associated with the transmitted signal, and the controller is configured to determine a separation distance between the mobile station and each base receiver that received the transmitted signal based at least upon the timing error, and is further configured to determine the location of the mobile station within the wireless communication network based upon the separation distance between the mobile station and the base receivers that received the transmitted signal,

the controller is configured to calculate a difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal, and

the controller is further configured to average the calculated difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal.

20. The wireless communication system of claim 19, wherein the controller is configured to subtract the averaged difference in the timing errors forwarded by each base receiver for each combination of base receivers that received the transmitted signal.

21. The wireless communication system of claim 20, wherein the controller is further configured to determine the separation distance between the mobile station and each base receiver that received the transmitted signal by dividing the subtracted averaged difference by a factor.

22. The wireless communication system of claim 21, wherein the controller is further configured to plot a circular region around a location of each base receiver that received the transmitted signal, each circular region having a radius equal to the separation distance between the mobile station and the respective base receiver, and is further configured to determine an intersection point of the plotted circular regions, thereby providing the location of the mobile station in the wireless communication network.

23. A method for determining a location of a mobile station within a wireless communication network, the wireless communication network including a plurality of base receivers coupled to a switch for receiving communication from the mobile station during a specified period of time, the method comprising:

transmitting a signal from the mobile station for receipt by a subset of the plurality of base receivers;

determining a timing error associated with the transmitted signal for each of the subset of base receivers that received the transmitted signal; and

determining the location of the mobile station within the wireless communication network as a function of the timing error, wherein determining a timing error further comprises;

determining a plurality of filter coefficients to match the signal transmitted by the mobile station to a predefined synchronous bit pattern,

continuously convolving the plurality of determined filter coefficients with the signal transmitted by the mobile station until a predefined recognition pulse is output by the convolution, and

determining a difference in time that the predefined recognition pulse is output and the specified time period that the mobile station should have transmitted the signal.

24. The method of claim 23, wherein determining a timing error further comprises:

determining a difference in time that the mobile station transmitted the signal and the specified time period that the mobile station should have transmitted the signal.

25. The method of claim 23, further comprising:

determining a separation distance between the mobile station and each base receiver that received the transmitted signal based at least upon the timing error; and

wherein determining the location of the mobile station further comprises determining the location of the mobile station within the wireless communication network based upon the separation distance between the mobile station and the base receivers that received the transmitted signal.

26. The method of claim 23, wherein determining a plurality of filter coefficients to match the signal transmitted by the mobile station to a predefined synchronous bit pattern further comprises:

removing a carrier frequency from the signal transmitted by the mobile station, thereby providing a resultant modulating signal;

computing a spectrum of the resultant modulating signal;

performing frequency domain filtering of the spectrum to derive a dual Hilbert transform, thereby determining a phase of an intermediate subsidiary function;

setting a magnitude of the intermediate subsidiary function;

correcting for non-causality and long-range causality of the intermediate subsidiary function; and

placing the removed carrier frequency back into the signal transmitted by the mobile station.